The capacity to perform activities of daily living or functional ability is critical to successful aging. Functional ability, immune function, skeletal integrity and cardiovascular indices decline in later life and are associated with leading sources of morbidity and mortality among older adults. Participation in physical activity, including regular exercise, has been found to be associated with increased functional ability, improved skeletal integrity, immune function and cardiovascular indices. A limited number of investigators have reported that older adults can preserve or enhance select measures of functional ability, skeletal integrity, immune function and cardiovascular indices through various types of exercise interventions. No study has yet compared the efficacy of regular aerobic walking, with dynamic strength training, with a combination of these two modes of exercise on functional ability, skeletal integrity, immune function or cardiovascular indices among older adults with limited functional ability. The findings of this study will provide a better understanding of the potency that these different modes of exercise training can have upon functional ability, skeletal integrity, immune function and cardiovascular indices among older adults. The specific aim of this study is: to compare the efficacy of 16 weeks of either dynamic strength training or aerobic walking or combined dynamics strength training and aerobic walking or a non-exercise control condition on functional ability, immune function, skeletal integrity, and cardiovascular fitness indices among adults aged 65 years and older who exhibit moderately limited functional abilities. One-hundred-and eighty-four subjects age 65 and older that report and exhibit below average functional ability will be recruited from the community. Subjects will be assessed prior to beginning interventions at baseline and again 8 and 16 weeks following the baseline testing. These assessments will include measures of functional ability, aerobic capacity, muscle strength, skeletal integrity, immune function and cardiovascular indices. Following baseline testing subjects will be randomized into a dynamic strength training group, an aerobic walking group, a combined dynamic strength training and aerobic walking group or a nonexercise control group. Subjects in the three exercise groups will participate in their respective prescribed treatment, three times per week for 16 weeks. The dynamic strength training protocol is designed to improve muscle strength. The aerobic walking protocol is designed to improve aerobic capacity. The combined strength and aerobic training intervention is designed to improve muscle strength and aerobic capacity. The four principle hypotheses of this study will be tested through repeated measures analysis of covariance. This statistic compares the four groups' dependent outcome measures at the 8 and 16-week retest while adjusting for dependent measures taken at baseline and potential confounding variables between the groups.